Why doesn't my boyfriend want to share his hobbies?

ok so my boyfriend has numerous hobbies like kayaking, flying, mountain biking, video games, sailing, water skiing which we've all done together and had a great time doing. im actually beginning to really take an interest in flying and would like to acquire my license. However there is 1 hobby which he has and id really love to have a chance to do it with him. its hang gliding. i asked him to take me but he always says no but maybe in the future. im not hurt, i know most guys wont even share 1 hobby with their gf so I am extremely happy however i am wondering why wont he do it if he already shares so much with me. i really want to try it, should i drop just a hint once in a while and hopefully he takes me one day?